M. Rodmar

Low temperature transport properties in high resistivity (i)-AlPdRe

Abstract The transport properties of icosahedral Al 70.5 Pd 21 Re 8.5 have been measured. Samples were prepared either by arc melting or by melt-spinning with subsequent annealing in both cases. Measurements of the resistivity were performed between 40 mK and 300 K and of the magnetoresistance up to 12 T from 0.2 K to 4 K. The resistivity was found to become constant at different temperatures between 0.2 and 2 K, but both the temperature dependence of the resistivity and the magnetoresistance differ at low temperatures for the two kinds of samples. The differences between the samples are briefly discussed. Our results indicate that the conductivity in AlPdRe remains finite at low temperatures in the present samples, and a metal–insulator transition cannot thus be confirmed from these measurements.

Transition from weak to strong electronic localization in icosahedral AlPdRe

Abstract In this paper we investigate when the transition from weak to strong localization takes place in icosahedral AlPdRe. This was made by determining an upper limit of the residual resistance ratio, RRR = ϱ 4.2 K /ϱ 295 K , where theories of quantum interference effects (QIE) can account for the magnetoresistance in these materials. It was found that QIE can describe the magnetoresistance in samples with RRR up to about 10. For samples with higher RRR several observations strongly suggest that other transport mechanisms have to be considered.

Magnetoresistance in the region of the possible metal–insulator transition in icosahedral AlPdRe

The magnetoresistance, Δρ(B,T)/ρ(T), has been measured between 200 mK and 20 K, in magnetic fields up to 12 T for icosahedral AlPdRe quasicrystals of nominal composition Al70.5Pd21.5Re8. Samples of varying resistivities and residual resistance ratios, R [=ρ(4 K)/ρ(295 K)], were studied. An analysis of Δρ(B,T)/ρ(T) in terms of quantum interference effects (QIE) was made, taking into account the possibility of QIE contributions to Δρ(T) up to room temperature. The results show that the regime of diffusive metallic conduction in i-AlPdRe extends up to R in the range of 20, corresponding approximately to ρ(4 K) up to 105 μΩ cm, beyond which a description of Δρ(B,T)/ρ(T) in terms of QIE breaks down.

Vanishing Coulomb interaction parameter Fσ with increasing temperature in AlCuFe-quasicrystals

Abstract The magnetoresistance of two icosahedral AlCuFe samples has been measured between 4.2 and 40 K in magnetic fields up to 12 T. From these data we determined the temperature dependence of the Coulomb interaction parameter, Fff, which scales the diffusion channel electron-electron interaction in quantum interference effects. F σ was found to decrease linearly with increasing temperature and to vanish at about 30 K.

Superconducting transition temperature in amorphous ReCr alloys

Abstract Superconductivity in a new amorphous alloy system, Re 1− x Cr x with x = 6, 14, 21, 31 and 42%, is reported. This system has an anomalous concentration dependence of the superconducting transition temperature; T c increases with increasing Re concentration, in contrast to the decrease expected from the average number of electrons per atom. We conjecture that these properties are due to short-range order, which is close to the σ-phase Re 60 Cr 40 , and a decrease in the electron-phonon interaction with increasing Cr content.